A mistrial was declared yesterday in a Manhattan love-triangle murder trial after the lone, pro-acquittal holdout suffered what her doctor called a “mental breakdown.”

The holdout suffered from anxiety, panic, tightening in the chest, shortness of breath and a dangerously high pulse rate, according to a doctor’s note read aloud by state Supreme Court Justice James Yates.

The doctor told the judge that not even drugs and a day of rest would get the jumpy juror back in the deliberations room – where seven men and five women had been deciding the fate of jealous, knife-wielding fiend Trevor Frederick.

Frederick, 26, is accused of attempting to murder his pretty ex, Jenae Aragosa, 20, by admittedly swinging a kitchen knife into her neck so hard, it nearly severed her spinal cord.

He is also accused of then driving Aragosa’s date of a single night, Christopher Mariconi, 23, out of Aragosa’s Upper West Side dorm room window to his death.

Aragosa had testified that just before she lost consciousness from her near-fatal knife wound, she heard Frederick snarl, “You made me kill my girlfriend,” and saw him take a step toward his tragic young rival.

The holdout had thrown a monkey wrench into deliberations for some time, according to notes sent back to the judge by the fractured jury.

Yesterday morning, she failed to show up entirely. When the judge reached her by phone at her home, she told him she was suffering from hives on the soles of her feet.

When the judge asked her if this had ever happened before, “She said on occasion, when she gets nervous,” the judge told the courtroom.

But when he asked her to return to deliberations, she balked.

“I said I will direct you to be here at 2 p.m.” he told the courtroom. “And then she hung up.”

The mistrial became inevitable once the juror’s doctor weighed in.

“The level of medication necessary to make her come back and even be able to face the courtroom . . . would be disabling,” Yates said of the doctor’s opinion on the panicky holdout.

The sudden, inconclusive end to the three-week trial left the victims’ family members collapsing in tears into each other’s arms.

Particularly distraught was Aragosa, who sobbed uncontrollably. The mistrial means Aragosa will likely have to retake the stand to testify against Frederick in a retrial, possibly early next year.